An electromagnetic shielding structure is, for example, used in a display, such as a plasma display.
A plasma display has a plasma gas mixture (Ne, Xe, Ar) trapped between two glass plates, and phosphors placed on the internal face of the rear plate of the display. Ultraviolet light radiation emitted by the plasma gas mixture during the plasma discharge between the two glass plates interacts with the phosphors on the internal face of the rear plate in order to produce the visible light radiation (red, green or blue). A gas particle deexcitation mechanism competes with the UV emission, which generates infrared radiation between 800 and 1250 nm, the propagation of which radiation, mainly through the front face of the display, may be the source of very troublesome interference, especially as regards equipment located nearby and controlled by infrared, for example by means of remote controls.
Moreover, like all electronic apparatus, plasma displays possess addressing systems (drivers) that may generate parasitic radiation which must not interfere with other devices, such as microcomputers, mobile telephones, etc.
To eliminate, or at the very least attenuate, the propagation of such radiation, one solution consists in placing against the front face of the display a structure that is both transparent and metallized in order to provide electromagnetic shielding.
A known example of a shielding structure, as illustrated in FIG. 1, comprises two glass substrates 10 and 11 between which two PVB thermoplastic sheets 12 and 13 and a PET sheet 14 are sandwiched, a copper mesh 15, constituting the conducting element for electromagnetically shielding the structure, being deposited by photolithography on the PET sheet 14, the latter being sandwiched between the two PVB sheets 12 and 13. The electrical connection of the copper mesh to ground is performed by means of flat conductors, such as busbars 16, soldered on one side to the copper mesh 15 and connected, on the other side, to a grounded metal frame 17. This metal frame constitutes the frame of the display and serves as support for the shielding structure associated with the display.
To keep the flat conductors 16 in position, for the purpose of soldering them to one of the faces of the copper mesh 15, the conductors form a return over the edge of the PET sheet 14 and the soldering takes place while the PET sheet and the PVB sheets are being joined together by heating the thermoplastics.
However, improper handling of the PVB sheets and/or incorrect joining of the PVB sheets to the PET sheet with the conductors may result in defects in the structure, such as blisters between the plastic sheets. Such defects are visible to the naked eye and such a product therefore cannot be used in displays.
In addition, the operation of folding the flat conductors over the edge of the PET sheet and of bonding them thereto, in a suitable manner and without any defects, in order to form the returns, is not a rapid step in an industrial manufacturing process. Furthermore, if this folding-over is poorly implemented, it may result in a breakage at the corner of the returns.
Consequently, the joint dependence of the electrical connection means, consisting of the flat conductors, on the conducting shielding element and on the PET backing sheet of the conducting shielding element does not allow the shielding structure to be easily manufactured.